Anti Sleep Alarm
Accident Patterns and Risk Factors
Type of Driver
Several studies have identified young male drivers, aged under 30 years, as one of the groups most at risk of being involved in sleep related road accidents. Horne found that about half of the drivers involved in sleep related accidents were males aged below 30 years, with the peak age being 21 - 25 years.
Maycock also found that young male drivers were at greater risk. This study identified company car drivers as having a high probability of falling asleep at the wheel because they tend to drive high mileage, on monotonous roads and have tight schedules.
A Danish study found that tiredness was common among young male drivers who were driving at night.
American studies have identified three main risk groups among drivers:
- male drivers aged 16 - 29 years
- shift workers
- people with sleep problems.
Another American study found that 55% of sleep related crashes involved drivers aged 25 years or younger, with the peak age being 20 years.
Untreated sleep apnea (brief interruptions of air flow and loss of oxygen while sleeping, resulting in poor and fragmented sleep) and narcolepsy (a disorder of the sleep-wake mechanism which can cause excessive daytime sleepiness) increase the risk of sleep related driving accidents. Many people with these conditions are undiagnosed and untreated, and are unaware of
their increased risk.
Time of Day
Sleep related accidents peak in the early hours of the morning, between 2:00 and 6:00 am, and in the mid afternoon, between 3:00 and 4:00 pm, due mainly to circadian rhythms. Horne calculated that drivers are 50 times more likely to fall asleep at the wheel at 2:00 am than at 10:00 am. The risk is three times as great between 3:00 - 4:00 pm than at 10:00 am.
There appears to be a link between the age of the driver and the peak fatigue time. Younger drivers are more prone to fatigue in the early hours of the morning, whereas older drivers are more likely to fall asleep at the wheel during the afternoon sleep period. For drivers aged 70 years or more, the peak time period was between 10:00 and 11:00 am.
Maycock also found a link between sleep related accidents and time of day, again with the highest risk period being the early hours of the morning.
American research also shows the same time pattern of sleep related accidents related to the age of the driver. Those aged up to 45 years were more at risk in the early hours, those aged between 45 and 65 years were most at risk around 7:00 am, and those aged over 70 years the peak period was 3:00 pm.
Type of Journey
Journeys involving long periods of driving on monotonous roads, such as motorways, are more likely to result in a driver falling asleep at the wheel. Journeys that are for work purposes, especially ones involving truck drivers or company car drivers, are also a high risk type of journey.
As discussed above, there is a clear relationship between time of day and the likelihood of falling asleep while driving. Therefore, journeys which involve driving in the early hours, and to a lesser extent in the middle of the afternoon, are likely to generate more risk.
Boredom; people who are under-stimulated tend to feel drowsy and more likely to fall asleep.
Type of Road
As noted above, roads which involve sustained, monotonous driving, with little visual stimulus for the driver, and where drivers are not required to attend to either the vehicle’s controls or respond to multiple road users and junctions, are more likely to have sleep related accidents. Urban roads are less prone to fatigue crashes because the level of activity is so much
greater, and helps to keep drivers active and alert.
Horne found two-thirds of sleep related accidents occurred on A roads, 9% on motorways, 16% on B roads and 9% on minor roads.
Maycock found higher rates on motorways (20%) and non built-up roads (14%) than on built-up roads (5%).
Other Impairment Factors
Lack of sleep is not the only cause of sleepiness. General health, alcohol, drugs, medicines and illness also cause tiredness, in addition to their other impairment effects. Most studies about driver fatigue exclude accidents where other impairment factors have been identified in order to isolate the effects of fatigue. However, sleepiness caused by alcohol or other drugs is
still influenced by the circadian rhythm, so that the effects of the alcohol or drug are likely to be greater during peak periods of sleepiness (the early hours and mid afternoon).
Research at Loughborough University shows that drinking alcohol in the early afternoon is about twice as likely to make a driver sleepy than the same amount drunk in the early evening.
Recent research in Australia and New Zealand suggests that staying awake for 17 - 19 hours results in the same level of impairment as drinking around 50 mg of alcohol, and produces much slower response speeds.
Type of Accident
Sleep related accidents tend to be more severe, possibly because of the higher speeds involved and because the driver is unable to take any avoiding action, or even brake, prior to the collision. Horne describes typical sleeprelated accidents as ones where the driver runs off the road or collides with another vehicle or an object, without any sign of hard braking before the impact.
Horne also suggests that the risk of death or serious injury to drivers may be greater in sleep related accidents than in other types of accident. A study of accidents in North Carolina also concluded that sleep related accidents tended to have more severe consequences.
Zomer found that the number of casualties in sleep related accidents was 50% higher than in all accidents, and sleep accidents had three times as many fatalities, and twice as many serious injuries, than non sleep related accidents.
Indications that an accident is sleep related are that :
- a single vehicle left the road
- the accident occurred on a high speed road
- the driver did not attempt to brake or swerve to avoid the accident
- the driver was alone in the vehicle
- the accident occurred in the early hours of the morning, or between 3:00 and 4:00 pm.